This invention relates to apparatus for processing a video signal, such as may be produced by a video camera or recorded/reproduced by a video tape recorder, and, more particularly, to such apparatus that controls various types of processing operations so as to impart optimum parameters and characteristics to the processed video signal.
Video signal processing of video signals generated or used by video equipment, such as a video camera or a video tape recorder, is well known. Typical types of such signal processing include gamma correction, contour correction, AGC control, black level adjustment, white balance adjustment, hue adjustment, color temperature adjustment, and the like.
Heretofore, when such video equipment, for example, a video camera, is preset for proper corrections and adjustments, the various correction and adjustment control parameters (e.g. a gamma correction control signal, an AGC control signal, a black level adjustment signal, etc.) are set before the video equipment is shipped for distribution, use or sale. The adjustment control parameters are determined as functions of different characteristics of the video signal produced by the video apparatus (e.g. the video signal produced by a video camera) and are established by an ancillary, add-on device that must be connected to the video equipment. Although the adjustment control parameters are determined externally of the-video equipment, such parameters are supplied to the video processing circuits included in the video equipment whereat such parameters are used to effect proper gamma correction, contour correction, AGC control, and the like.
An example of how such ancillary parameter-calculating apparatus is used with video equipment, such as a video camera, is illustrated in FIG. 5. For convenience, the video camera is assumed to include a CCD image sensor 90 as the image pickup unit, but it is known that other conventional image pickup devices may be used. The image signal produced by pickup unit 90 is supplied to and processed by a video signal processor 91, which executes gamma correction, contour correction, white balance adjustment, hue adjustment, and various other video control and adjustment operations. As a result, the video signal processor produces a luminance signal Y and a chroma signal C, both properly corrected and adjusted.
The operating levels or parameters for gamma correction, contour correction, white balance adjustment, hue adjustment, etc. of video signal processor 91 are derived from control data stored in a programmable read only memory 92, such as an EEPROM, or other non-volatile memory. Such stored control data are read out from the memory by a system controller 93, converted to analog form by a digital-to-analog (D/A) converter 94 and supplied to the individual processing circuits included in video signal processor 91. Thus, depending upon the values of the control data stored in EEPROM 92, the corresponding corrections and adjustments in the video signal produced by pickup unit 90 are made by video signal processor 91.
To generate the proper control data to be stored in EEPROM 92, the luminance and chrominance signals Y and C produced by the video camera are analyzed. Such analysis is made by an external adjustment apparatus 100 which, as shown in FIG. 5, is electrically connected to the video camera. The adjustment apparatus includes a microprocessor 103 that is suitably programmed to calculate the individual control and adjustment parameters to obtain optimum gamma correction, contour correction, white balance adjustment, hue adjustment, etc. This is achieved by digitizing the luminance and chrominance signals produced by the video camera and detecting the digitized video signals by a wave detector 102. In this regard, an analog-to-digital (A/D) converter 101 is selectively coupled by way of a switch to receive either the luminance signal Y or the chroma signal C and to digitize the luminance and chroma signals supplied thereto. Wave detector 102 is coupled to A/D converter 101 and detects level information and phase information of the digitized luminance signal Y and the digitized chroma signal C. It is this detected level and phase information that is supplied to microprocessor 103 and used thereby to calculate the different control parameters needed to effect optimum gamma correction, contour correction, white balance adjustment, hue adjustment, etc. For example, if the detected level and phase information differ from predetermined reference levels, the microprocessor calculates those control parameters which, when supplied to video signal processor 91, result in corrections and adjustments to the video signal such that the level and phase information that is detected by wave detector 102 is substantially equal to such predetermined reference levels. It is seen that the calculated control parameters are supplied from microprocessor 103 of adjustment apparatus 100 to D/A converter 94 included in the video camera, whereat such control parameters are converted to analog form and used by video signal processor 91 for gamma correction, contour correction, etc. The closed loop formed of the video signal processor, A/D converter 101, wave detector 102, microprocessor 103 and D/A converter 94 operates such that optimum control parameters are generated by the microprocessor; and these control parameters are written into memory 92 by system controller 93. Thereafter, adjustment apparatus 100 may be disconnected from the video camera; but the control parameters stored in memory 92 nevertheless control video signal processor 91 to carry out optimum control and adjustment operations on the video signal derived from pickup unit 90.
It is apparent that the prior art arrangement shown in FIG. 5 does not permit's resetting or readjustment of the control parameters stored in memory 92 once adjustment apparatus 100 is disconnected from the video camera. Thus, modifications or resetting of such control parameters, which may be needed over a period of time, are not easily attainable without reconnecting adjustment apparatus 100. Such adjustment apparatus often is quite expensive and is constructed as a rather large piece of equipment, thus making it expensive and inconvenient to sell such adjustment apparatus along with the video camera with which it may be used. Alternatively, if the adjustment apparatus normally is furnished only to skilled technicians, it may be difficult, bothersome and expensive for the user of the video camera to seek the assistance of such technicians for occasional resetting of the control parameters. Thus, the quality of the video signal produced by the video camera may deteriorate because adjustments to the control parameters used by the video signal processor are not made.
The foregoing difficulties are equally applicable to other video equipment, such as video tape recorders, that include video signal processors which are supplied with control parameters that may require adjustment from time to time.